The present invention relates to a plasma processing method for use in a fabrication process of semiconductor devices, and more particularly relates to a plasma processing method, by which an etching or deposition process is carried out using plasma created from fluorocarbon gas.
In recent years, downsizing of semiconductor devices has accelerated so much that the required pattern definition is on the verge of reaching the 0.1 xcexcm order at last.
However, the fabrication process of semiconductor devices is basically no different from what it used to be. That is to say, first, a thin film is deposited on a semiconductor substrate. Next, a resist film (i.e., an organic film) is defined on the thin film by a photolithographic process. And then the thin film is etched using the resist film.
Nevertheless, the type of exposing radiation, typically adopted in a lithographic process, has lately changed from line into KrF or ArF excimer laser radiation to cope with the accelerating downsizing trend of semiconductor devices. In addition, organic resist films have also been developed responsive to the change of exposing radiation.
The application of the ArF excimer laser radiation as exposing radiation to the 0.1 xcexcm-order patterning is now under research and development. However, it is known that an organic resist film would be poorly resistant to an etching process in that case.
Thus, to ensure a high selectivity with respect to the resist film, various techniques have been proposed. For example, a technique takes advantage of a property of a silicon material as a fluorine scavenger by making a member inside a reaction chamber out of the silicon material. That is to say, according to the technique, the selectivity against the resist film can be improved by decreasing the concentration of fluorine in an etching gas.
Hereinafter, a known plasma processing method will be described with reference to FIG. 1.
FIG. 1 illustrates a schematic construction of an inductively coupled plasma processing system. As shown in FIG. 1, the inner walls of a reaction chamber 10 are covered with quartz plates 11. An induction coil 12 is wound around the outside of the reaction chamber 10. One end of the induction coil 12 is connected to a first RF power supply 13, while the other end of the induction coil 12 is grounded.
A gas inlet port 14 of the reaction chamber 10 is connected to a gas supply source (i.e., gas cylinder) 16 via a mass flow controller 15. A gas outlet port 17 of the reaction chamber 10 is connected to an exhaust pump 19 by way of a pressure control valve 18. Accordingly, the gas pressure inside the reaction chamber 10 is controlled using the mass flow controller 15 and/or the pressure control valve 18 and exhaust pump 19.
A sample stage 20, which will be a lower electrode, is provided inside the reaction chamber 10 and connected to a second RF power supply 22 by way of a matching circuit 21.
A control unit 23 provides control signals to the first and second RF power supplies 12 and 22, mass flow controller 15 and pressure control valve 18. In this manner, the unit 23 controls first RF power supplied from the first RF power supply 12 to the induction coil 12, second RF power supplied from the second RF power supply 22 to the sample stage 22, the flow rate of the gas supplied from the gas supply source. 16 to the reaction chamber 10 and that of the gas exhausted from the reaction chamber 10.
The gas pressure inside the reaction chamber 10 is normally controlled to a predetermined value between 0.133 and 1.33 Pa by adjusting the pressure control valve 18 with the exhaust pump 19 operated continuously.
The first RF power is applied from the first RF power supply 13 to the induction coil 12 with a process gas supplied through the gas inlet port 14 into the reaction chamber 10 and with the gas pressure inside the reaction chamber 10 kept at the predetermined value. In this manner, plasma is created from the process gas. Thereafter, the second RF power is applied from the second RF power supply 22 to the sample stage 20, thereby getting the created plasma attracted to a semiconductor substrate that has been placed on the sample stage 20. As a result, a thin film, which has been formed on the surface of the semiconductor substrate, is etched or a thin film is deposited on the surface of the semiconductor substrate.
As described above, a silicon material functions as a fluorine scavenger. Accordingly, if an etching gas containing fluorine is introduced into the reaction chamber 10, then silicon, which is the material of the sample stage 20 and a silicon ring (not shown), combines with that fluorine to produce SiFx (where x=3 or 4). In this manner, the concentration of fluorine in the etching gas is adjustable and therefore the etch rate is controllable. It is well known that the concentration of fluorine affects the etch rate of a resist film.
Thus, Japanese Laid-Open Publication No. 10-98024 suggests that a fluorocarbon gas, in which the ratio of carbon to fluorine (which will be herein called a xe2x80x9cC/F ratioxe2x80x9d) is relatively high (e.g., C5F8 gas), is preferably used to increase the selectivity of a silicon dioxide film being dry-etched (or plasma-etched) to a resist film used as a mask.
However, when the present inventors dry-etched a silicon dioxide film using the C5F8 gas with a high C/F ratio and masking the silicon dioxide film with a resist film, we didn""t find that the resultant selectivity increased compared to the conventional C2F6 gas with a low C/F ratio.
We carried out the experiment in the following manner.
An ICP plasma-enhanced dry etching system was used as an etching system. The power applied to create plasma was set at 1600 W. A mixture of C5F8 and Ar gases was used as an etching gas. The flow rates of the C5F8 and Ar gases were defined at 4.7 and 4.0 ml/min, respectively. And the gas pressure was set at 1.33 Pa. A silicon dioxide film was etched using a resist film as a mask under the process conditions such as these.
As a result, although a gas with a high C/F ratio (i.e., the C5F8 gas) was used, the selectivity against the resist film was just 1.81, which is not so much different from that of the conventional gas with a low C/F ratio (e.g., C2F6 gas).
In view of these, an object of the present invention is increasing the selectivity attained when dry etching is carried out using a fluorocarbon gas with a C/F ratio of 0.5 or more.
The present inventors believe that if a silicon dioxide film is dry-etched using a fluorocarbon gas with a high C/F ratio, the selectivity thereof to a resist film increases because of the following reason. Specifically, we believe that a polymer film would be deposited on the surfaces of the silicon dioxide and resist films and decrease the etch rates. Accordingly, if the decrease in etch rate of the silicon dioxide film is less than the decrease in etch rate of the resist film, then the selectivity to the resist film would increase. On the other hand, if the decrease in etch rate of the silicon dioxide film is equal to or greater than the decrease in etch rate of the resist film, then the selectivity to the resist film would not increase.
Thus, the selectivity to the resist film does not always increase by the use of a fluorocarbon gas with a high C/F ratio. More exactly, the selectivity to the resist film can be increased not only by using the fluorocarbon gas with the high C/F ratio but also by making the etch rate of the silicon dioxide film decrease less than the etch rate of the resist film.
Furthermore, we paid special attention to the residence time xcfx84 of the fluorocarbon gas, which is given by Pxc3x97V/Q, where P is the pressure (unit: Pa) of the fluorocarbon gas, V is the volume (unit: L) of the reaction chamber and Q is the flow rate (unit: Paxc2x7L/sec) of the fluorocarbon gas. By applying numerous combinations of pressures and flow rates of the fluorocarbon gas to reaction chambers with various volumes, we tried to find the residence times xcfx84 at which the selectivity to the resist film increases. As a result, we found that where a fluorocarbon gas with a C/F ratio of 0.5 or more was used, the selectivity to the resist film increased if the residence time xcfx84 was greater than 0.1 sec and equal to or less than 1 sec. That is to say, we found that the selectivity to the resist film did not increase if the residence time xcfx84 was equal to or less than 0.1 sec. This means that the deposition of the polymer film accelerated (i.e., the deposition rate of an organic film increased) in that situation.
As can be seen from the equation for the residence time xcfx84=Pxc3x97V/Q, the residence time xcfx84 changes with the volume V of the reaction chamber.
Thus, we also found that if Pxc3x97W0/Q, which is a product of the residence time (i.e., xcfx84=Pxc3x97V/Q) and the density Pi of power applied to create plasma (i.e., Pi=W0/V, where W0 is the magnitude of the power and v is the volume of the reaction chamber), is used, the selectivity to the resist film or the deposition rate of the organic film can be increased irrespective of the volume of the reaction chamber.
The basic idea of the present invention was acquired from these findings. Specifically, the scope of the present invention is defined as follows.
A first inventive plasma processing method includes the steps of: placing a substrate inside a reaction chamber of a plasma processing system, a silicon dioxide film having been formed on the surface of the substrate; introducing a fluorocarbon gas, which contains carbon and fluorine and in which a ratio of carbon to fluorine is 0.5 or more, into the reaction chamber; and creating a plasma from the fluorocarbon gas and etching the silicon dioxide film with the plasma. A residence time xcfx84 of the fluorocarbon gas in the reaction chamber is controlled at a value greater than 0.1 sec and equal to or less than 1 sec. The residence time xcfx84 is given by Pxc3x97V/Q, where P is a pressure (unit: Pa) of the fluorocarbon gas, V is a volume (unit: L) of the reaction chamber and Q is a flow rate (unit: Paxc2x7L/sec) of the fluorocarbon gas.
In the first plasma processing method, the silicon dioxide film is etched with the residence time xcfx84 of the fluorocarbon gas in the reaction chamber controlled at a value greater than 0.1 sec and equal to or less than 1 sec. Thus, the selectivity to the resist film can be increased to two or more with the process stabilized.
A second inventive plasma processing method includes the steps of: placing a substrate inside a reaction chamber of a plasma processing system, a silicon dioxide film having been formed on the surface of the substrate; introducing a fluorocarbon gas, which contains carbon and fluorine and in which a ratio of carbon to fluorine is 0.5 or more, into the reaction chamber; and creating a plasma from the fluorocarbon gas and etching the silicon dioxide film with the plasma. Pxc3x97W0/Q is controlled at a value greater than 0.8xc3x97104 secxc2x7W/m3 and equal to or less than 8xc3x97104 secxc2x7W/m3. Pxc3x97W0/Q is a product of a residence time xcfx84 of the fluorocarbon gas in the reaction chamber and a power density Pi of power applied to create the plasma. The residence time xcfx84 is given by Pxc3x97V/Q, where. P is a pressure (unit: Pa) of the fluorocarbon gas, V is a volume (unit: L) of the reaction chamber and Q is a flow rate (unit: Paxc2x7L/sec) of the fluorocarbon gas. The power density Pi is given by W0/V, where W0 is a magnitude (unit: W) of the power and V is the volume (unit: L) of the reaction chamber.
In the second plasma processing method, the silicon di-oxide film is etched with Pxc3x97W0/Q, which is a product of a residence time xcfx84 of the fluorocarbon gas in the reaction chamber and a power density Pi of power applied to create the plasma, controlled at a value greater than 0.8xc3x97104 secxc2x7W/m3 and equal to or less than 8xc3x97104 secxc2x7W/m3. Thus, the selectivity to the resist film can be increased to two or more with the process stabilized.
A third inventive plasma processing method includes the steps of: placing a substrate inside a reaction chamber of a plasma processing system; introducing a fluorocarbon gas, which contains carbon and fluorine and in which a ratio of carbon to fluorine is 0.5 or more, into the reaction chamber; and creating a plasma from the fluorocarbon gas and depositing an organic film on the substrate using the plasma. A residence time xcfx84 of the fluorocarbon gas is controlled at 0.1 sec or less. The residence time xcfx84 is given by Pxc3x97V/Q, where P is a pressure (unit: Pa) of the fluorocarbon gas, V is a volume (unit: L) of the reaction chamber and Q is a flow rate (unit: Paxc2x7L/sec) of the fluorocarbon gas.
In the third plasma processing method, an organic film is deposited with the residence time xcfx84 of the fluorocarbon gas in the reaction chamber controlled at 0.1 sec or less. Thus, the deposition rate of the organic film can be increased with the process stabilized.
A fourth inventive plasma processing method includes the steps of: placing a substrate inside a reaction chamber of a plasma processing system; introducing a fluorocarbon gas, which contains carbon and fluorine and in which a ratio of carbon to fluorine is 0.5 or more, into the reaction chamber; and creating a plasma from the fluorocarbon gas and depositing an organic film on the substrate using the plasma. Pxc3x97W0/Q is controlled at 0.8xc3x97104 secxc2x7W/m3 or less. Pxc3x97W0/Q is a product of a residence time xcfx84 of the fluorocarbon gas and a power density Pi of power applied to create the plasma. The residence time xcfx84 is given by Pxc3x97V/Q, where P is a pressure (unit: Pa) of the fluorocarbon gas, V is a volume (unit: L) of the reaction chamber and Q is a flow rate (unit: Paxc2x7L/sec) of the fluorocarbon gas. The power density Pi is given by W0/V, where W0 is a magnitude (unit: W) of the power and V is the volume (unit: L) of the reaction chamber.
In the fourth plasma processing method, an organic film is deposited with Pxc3x97W0/Q, which is a product of a residence time xcfx84 of the fluorocarbon gas in the reaction chamber and a power density Pi of power applied to create the plasma, controlled at 0.8xc3x97104 secxc2x7W/m3 or less. Thus, the deposition rate of the organic film can be increased with the process stabilized.
In the first through fourth plasma processing methods, the fluorocarbon gas is preferably a gas containing at least one of C4F8, C4F6, C3F8, C5F8 and C6F6 gases.
In the first through fourth plasma processing methods, the residence time xcfx84 is preferably controlled by a mass flow controller provided for the plasma processing system and/or a valve and a pump provided for the plasma processing system.
A fifth inventive plasma processing method includes the steps of: placing a substrate inside a reaction chamber of a plasma processing system, a silicon dioxide film having been formed on the surface of the substrate; introducing a first fluorocarbon gas, which contains carbon and fluorine and in which a ratio of carbon to fluorine is 0.5 or more, into the reaction chamber; creating a first plasma from the first fluorocarbon gas and etching the silicon dioxide film with the first plasma; introducing a second fluorocarbon gas, which contains carbon and fluorine and in which a ratio of carbon to fluorine is 0.5 or more, into the reaction chamber; and creating a second plasma from the second fluorocarbon gas and depositing an organic film on the etched silicon dioxide film using the second plasma. A first residence time xcfx841 of the first fluorocarbon gas in the reaction chamber is controlled at a value greater than 0.1 sec and equal to or less than 1 sec. The first residence time xcfx841 is given by P1xc3x97V/Q1, where P1 is a pressure (unit: Pa) of the first fluorocarbon gas, V is a volume (unit: L) of the reaction chamber and Q1 is a flow rate (unit: Paxc2x7L/sec) of the first fluorocarbon gas. A second residence time xcfx842 of the second fluorocarbon gas in the reaction chamber is controlled at 0.1 sec or less. The second residence time xcfx842 is given by P2xc3x97V/Q2, where P2 is a pressure (unit: Pa) of the second fluorocarbon gas, V is the volume (unit: L) of the reaction chamber and Q2 is a flow rate (unit: Paxc2x7L/sec) of the second fluorocarbon gas. In the fifth plasma processing method, the selectivity to the resist film can be increased to two or more and the deposition rate of the organic film can also be increased with the process stabilized.
A sixth inventive plasma processing method includes the steps of: placing a substrate inside a reaction chamber of a plasma processing system, a silicon dioxide film having been formed on the surface of the substrate; introducing a first fluorocarbon gas, which contains carbon and fluorine and in which a ratio of carbon to fluorine is 0.5 or more, into the reaction chamber; creating a first plasma from the first fluorocarbon gas and etching the silicon dioxide film with the first plasma; introducing a second fluorocarbon gas, which contains carbon and fluorine and in which a ratio of carbon to fluorine is 0.5 or more, into the reaction chamber; and creating a second plasma from the second fluorocarbon gas and depositing an organic film on the etched silicon dioxide film using the second plasma. P1xc3x97W1/Q1 is controlled at a value greater than 0.8xc3x97104 secxc2x7W/m3 and equal to or less than 8xc3x97104 secxc2x7W/m3. P1xc3x97W1/Q1 is a first product of a first residence time xcfx841 of the first fluorocarbon gas in the reaction chamber and a power density Pi1 of first power applied to create the first plasma. The first residence time xcfx841 is given by P1xc3x97V/Q1, where P1 is a pressure (unit: Pa) of the first fluorocarbon gas, V is a volume (unit: L) of the reaction chamber and Q1 is a flow rate (unit: Paxc2x7L/sec) of the first fluorocarbon gas. The power density Pi1, is given by W1/V, where W1 is a magnitude (unit: W) of the first power and V is the volume (unit: L) of the reaction chamber. And P2xc3x97W2/Q2 is controlled at 0.8xc3x97104 secxc2x7W/m3 or less. P2xc3x97W2/Q2 is a second product of a second residence time xcfx842 of the second fluorocarbon gas in the reaction chamber and a power density Pi2 of second power applied to create the second plasma. The second residence time xcfx842 is given by P2xc3x97V/Q2, where P2 is a pressure (unit: Pa) of the second fluorocarbon gas, V is the volume (unit: L) of the reaction chamber and Q2 is a flow rate (unit: Paxc2x7L/sec) of the second fluorocarbon gas. The power density Pi2 is given by W2/V, where W2 is a magnitude (unit: W) of the second power and V is the volume (unit: L) of the reaction chamber.
In the sixth plasma processing method, the selectivity to the resist film can be increased to two or more and the deposition rate of the organic film can also be increased with the process stabilized.
In the fifth or sixth plasma processing method, the first fluorocarbon gas is preferably a gas containing at least one of C4F8, C3F8, C5F8 and C6F6 gases, while the second fluorocarbon gas is preferably a gas containing at least one of C4F8, C4F6, C3F8, C5F8 and C6F6 gases.
In the fifth or sixth plasma processing method, each of the first and second residence times xcfx841 and xcfx842 is preferably controlled by a mass flow controller provided for the plasma processing system and/or a valve and a pump provided for the plasma processing system.